The proposed research is to examine and to delineate physiologic regulation (neuroendocrine function) and tissue injury (serum enzymes) in microwave-exposed rats free of non-specific stresses. The quantitative relation among power density, body temperature and neuroendocrine function or tissue injury will be assessed. Specific attention will be paid to the interrelationships of hypothalamic-hypophysial/thyroid/adrenal/somatotrophic axes in the animal subjected to microwave exposure. The interaction of previous exposure on responses or injuries of rats to subsequent exposure will be investigated. Recovery or manifestation of acute neuroendocrine perturbance and tissue by microwave exposure will be examined. Neuroendocrine relation to body temperature will be the basis for determination of specific microwave effects if such specificity of microwave exposure occurs. Rats will be acclimated to experimental procedures. A 3-hour equilibrium period will be given before each microwave exposure. The proposed project will extend from single to repeated exposure to 2450 MHz microwave in the far-field at 0.1 to 40 mW/cm2 or the equivalent absorption rate. The duration of each exposure will be four hours.